Chromatin immunoprecipitation of mouse cortices was performed with the ChIP-IT High Sensitivity® Kit (Active Motif, cat. no 53040) according to the manufacturer's protocol. Frozen mouse cortices were cut into ~1 mm cubes in 10 mL Complete Tissue Fixation Solution in a 100-mm petri dish and incubated, with rotation, at room temperature for 15. The reaction was quenched with 515 µL Stop Solution followed by incubation at room temperature for 5 minutes. The cross-linked tissues were then homogenized by passing the suspension 20 times through a 20-guage needle attached to a sterile plastic syringe. The tissues were pelleted by centrifugation at 1,250 x g for 3 min at 4 °C and pellets were washed twice with 10 mL ice-cold PBS Wash Buffer. Washed pellets were resuspended in 5 mL Chromatin Prep Buffer supplemented with 5 µL protease inhibitor cocktail (PIC) and 5 µL 100 µM PMSF, incubated on ice for 10 minutes, and homogenized again to lyse cell membranes. Nuclei were pelleted by centrifugation as before, resuspended in 1 mL ChIP buffer, incubated for 10 min on ice, and sonicated in a Bioruptor (Diagenode) sonicator in 200 µL aliquots, each receiving 6 10-min rounds of sonication at high power (30 sec on / 30 sec off). Sonicated samples were clarified by centrifugation for 2 minutes at 4 °C at 16,000 x g and stored at -80 °C. Input DNA was prepared as follows: 25 µL was removed and purified according to the manufacturer's protocol (briefly, RNAse A treatment, Proteinase K treatment, addition of NaCl and reverse cross-linking at 65 °C for 16 hours, and purification by phenol:chloroform and ethanol extraction) and quantified using a NanoDrop spectrophotometer. 30 µg sheared chromatin was immunoprecipitated overnight at 4 °C by dilution in 200 µL ChIP Buffer supplemented with 5 µL PIC and incubation with 4 µg antibody with 5 µL Blocker. 30 µL washed Protein G agarose beads were added to the reaction and incubated for 3 h. The reactions were then diluted by the addition of 600 µL ChIP buffer and added to ChIP filtration columns, washed 5 times with Wash Buffer AM1, and eluted in 100 µL Elution Buffer AM4. ChIP DNA was purified in the same manner as input DNA and in 36 µL elution volume for ChIP-sequencing. Libraries were generated from 25 µL of fragmented DNA (range 100-300 bp) using the NEBNext Ultra II DNA Library Prep Kit for Illumina (NEB), as per the manufacturer's recommendations. Adapters and PCR primers were purchased from Integrated DNA Technologies (IDT). Size selection was carried out using SparQ beads (QIAGEN) prior to PCR amplification (12 cycles). Libraries were quantified using the KAPA Library Quanitification Kits - Complete kit (Universal) (Kapa Biosystems). Average fragment size was determined using a LabChip GX (PerkinElmer) instrument. The libraries were normalized, pooled, and then denatured in 0.05 N NaOH and neutralized using HT1 buffer. The pool was loaded at 175 pM (HEK293 cells) or 200pM (mouse cortices) on a Illumina NovaSeq S4 lane using Xp protocol as per the manufacturer's recommendations. The run was performed for 2x100 cycles (paired-end mode). A phiX library was used as a control and mixed with libraries at 1% level.